Gating circuit for selecting synchronization pulses to trigger an oscilloscope

ABSTRACT

The oscilloscope triggering circuit translates a composite video television signal to derive selected synchronization pulses which are used to trigger the horizontal sweep of an oscilloscope trace so that waveforms applied to the vertical input of the oscilloscope and which occur in time relation with the selected pulses are displayed thereon.

United States Patent [72] Inventor [56] References Cited UNITED STATESPATENTS 4/1970 LaPorta........................

Roger A. Swanberg Bensenville, Ill. [21] AppLNo. 823,409

May 9, 1969 [45] Patented Apr. 6, 1971 Primary Examiner-Rodney D.Bennett, Jr.

M t ol I Assistant ExaminerBrian L. Ribando Franklin P rk, Ill,AttorneyMueller, Aichele and Rauner GATING CIRCUIT FOR SELECTINGSYNCHRONIZATION PULSES T0 TRIGGER AN OSCILLOSCOPE mm .m H mm 0m men cs mSUhF HUM UUU [22] Filed [73] Assignee INTEGRATING NET.

I :ISI 1 I542 I38 J law-Ju ie MPAFE use JENABLING cmcun I I FIRST I IPLLEI GATING CIRCUIT FOR SELECTING SYNCHRONIZATION PULSES TO TRIGGER ANOSCILLOSCOPE BACKGROUND OF THE INVENTION The synchronizing (sync) signaltrain for controlling the timing of the scan of an electron beam in acathode-ray tube of a television receiver is comprised of horizontal,vertical, and equalizing pulses which all have about the same amplitude.Since the triggerable firing circuitry which sweeps the electron beam inan ordinary oscilloscope is sensitive only to the amplitude of anexternal trigger signal applied thereto, the firing circuitry cannotdistinguish between successive ones of these sync pulses. Consequently,the ordinary oscilloscope cannot easily be directly fired by theoccurrence of a given single sync pulse in each field or a particulargroup of successive sync pulses so that waveforms occurring in close orequal time relation in each field or field to field therewith can bedisplayed on the scope.

The foregoing limitation of the ordinary oscilloscope makes many timingand other waveform measurements related to the electrical operation oftelevision receivers difficult, and in some cases impossible, to make.When solving scan interlace problems, for example, it is sometimesdesirable to very accurately measure the time interval between thelagging edge of the vertical yoke current waveform for a first field ina frame and the lagging edge of the vertical yoke current waveform forthe successive or immediately following second field. Because the periodof each vertical sawtooth is on the order of 500 times the time intervalto be measured and because the time axis of the graticule of the scopeis only about centimeters long, the required accuracy of the measurementof the time interval is extremely difficult to achieve when the scope istriggered directly from the sawtooth waveforms themselves. To make thedesired measurement it would be advantageous if the oscilloscope couldbe triggered on the horizontal sync pulse immediately preceding theleading edge of the vertical blanking pulse of each vertical field. Thetrigger and sweep speed controls of the scope would be set so that thebeam of the scope is fired by the horizontal sync pulses somewhere nearthe termination of the first vertical sawtooth so that the beam wouldtrace only the termination of the first vertical sawtooth waveform andthe beginning of the second vertical sawtooth for each field therebyenabling the two lagging edges to be displayed simultaneously in timerelation to the horizontal sync, and the time difference between thewaveforms to fill most of the graticule so that the measurement of thetime interval between given current levels of the vertical yokewaveforms in succeeding fields, with respect to horizontal sync, can beaccurately performed.

Furthermore, in testing and designing color television receivers, acolor bar composite video signal wherein each field may contain sixgroups of about 40 identical scan lines is introduced into the circuitryto be tested. The processing of the color bar signal is then observed atvarious stages in the circuitry by use of an oscilloscope. Someoscilloscopes having a second time base can select and display the videosignal for a given horizontal line of the processed color bar signalwhen the scope is adjusted to have a comparatively low horizontal sweeprate. The resulting image on the oscilloscope, however, is too dim to beadequately seen when it is expanded by increasing the sweep rate so thatthe operator can view the transients, for instance, between two colorbursts on the same horizontal line of the color bar signal. If the scopecould be triggered by several selected horizontal sync pulses occurringin coincidence with the beginning of the scan lines of a given one ofthe six groups, then the associated video signal would be traced andretraced by the beam of the scope when its sweep rate was high. Thistracing and retracing would result in substantial trace brighteningbecause of the superposition of the image so that otherwise unseendetails of the waveform can be distinguished.

SUMMARY OF THE INVENTION invention It is one object of" the invention toimprove triggering circuits for an oscilloscope.

Another object of one embodiment of the invention is to provide anoscilloscope triggering system that will deliver a trigger signal orsuccessive trigger signals to fire an oscilloscope in time coincidencewith the respective occurrence of a selected television synchronizationpulse or pulses.

Still another object of one embodiment of the invention is to provide anoscilloscope triggering system that will select any single one orplurality of successive synchronization pulses from a televisioncomposite video signal and apply them to the trigger input of anoscilloscope so that the oscilloscope can be selectively triggeredthereby.

The oscilloscope triggering circuit of the invention provides triggersignals by allowing only selected ones or selected groups of successivesync pulses from a composite video signal to be applied to the triggerinput of an oscilloscope. The sync pulses are first clipped from acomposite video television signal and applied to one input of a dualinput gate and to a separating circuit which separates out the verticalsync pulses. A first timing circuit is triggered by the termination ofeach vertical sync pulse to produce a delay pulse whose time durationcan be adjusted. The termination of this delay pulse, in turn, triggersan enabling circuit to produce a delayed enabling pulse of adjustableduration which is applied to the other input of the dual input gate.Whatever synchronization pulses are applied to the gate during the timeduration of the enable pulse are allowed to pass through the gate totrigger the oscilloscope. Therefore, by adjusting the time duration ofthe delaying pulse the beginning of the enable signal with reference toeach vertical sync pulse can be established; and by adjusting the pulseduration of the enabling pulse itself any desired sync pulse orsuccessive pulses occurring subsequent to the beginning of the enablingsignal will pass through the gate to trigger the oscilloscope. Theseselected trigger signals facilitate observation on the oscilloscope ofselected periodic waveforms occurring in close or equal time relationtherewith.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a combination block andschematic diagram of a preferred embodiment of the invention; and FIG. 2is a timing diagram for illustrating the operation of a preferredembodiment of the invention and it includes the following:

FIG. 2A is an illustration of selected portions of a composite videotelevision signal;

FIG. 2B is an illustration of synchronizing pulses removed from thecomposite video signal of FIG. 2A;

FIG. 2C shows a vertical sync pulse whose serrations have been removed;

FIG. 2D shows the results of differentiating the vertical sync pulse ofFIG. 2C;

FIG. 2E shows the positive-going output pulse of the first timingcircuit;

FIG. 2F illustrates the results of differentiating the delay pulse ofFIG. 2E;

FIG. 2G shows the enabling pulse of the enabling circuit;

and

FIG. 2H is a timing diagram illustrating one application of theoscilloscope triggering system.

DESCRIPTION OF THE PREFERRED EMBODIMENT The oscilloscope triggeringcircuit utilizes a composite video television signal to allow only achosen sync pulse or a particular group of chosen successive sync pulsesthereof to be applied to the horizontal sweep trigger input of anoscilloscope. The general operation of the oscilloscope triggeringcircuit will first be described in reference to FIGS. 1 and 2 and then amore specific description will be given. Referring to FIG. 1, inverter10, amplifier I2, and sync stripper 14 operate to remove the horizontal,vertical and equalizing pulses from a composite television signal likethat of FIG. 2A applied to an input 15. These synchronization signals,shown in FIG. 2B, are applied from the output of sync stripper 14 toinput 16 of NAND gate 18 and to integrating network 20 which passes mostreadily the vertical synchronization pulses, illustrated in FIG. 2C, topulse amplifier 22. After differentiating circuit 23 differentiates eachresulting vertical sync pulses into a positive and a negative spike asshown in FIG. 20, the negative spike which is coincident with thetermination of the vertical sync pulse is utilized to switch firstvariable monostable multivibrator or delay circuit 24 into itsquasi-stable state thereby providing a rectangular pulse of FIG. 2Ewhose lagging edge occurs an adjustable time A after the termination ofthe vertical sync pulse. Each rectangular pulse is differentiated bycircuit 25 and the negative-going portion thereof, which corresponds toits termination as illustrated in FIG. 2F, is used to trigger a secondadjustable monostable multivibrator or enabling circuit 26. While theenabling circuit is in its quasistable state an enabling pulse, see FIG.20, is applied to input 28 of NAND gate 18. In response to this enablingpulse, NAND gate 18 allows whatever synchronizing pulses are beingapplied during the time interval or period thereof, from sync stripper14, to pass through the gate and be applied to trigger input 30 ofoscilloscope 32.

Therefore, the output pulse of enabling circuit 26 forms an adjustableelectrical window which selects sync pulses for selectively triggeringan oscilloscope. The leading edge of the window occurs a predeterminedtime after each vertical synchronizing pulse as established by theadjustable delay time of the delay circuit 24, and, the width of thewindow is deter mined by the adjustable recycle time of the enablingcircuit 26. Thus by adjusting the delay time of delay circuit 24 thebeginning portion of a synchronizing pulse train is selected and byadjusting the recycle time of enabling circuit 26 the number of syncpulses in the selected portion is determined. The selected sync pulse orgroup of successive pulses triggers the oscilloscope so that selectedwaveforms which are applied to its vertical input terminals 33 and 35and which occur in equal or close time relation to the selected triggerpulses can be displayed on the oscilloscope.

A more detailed description of the aforementioned circuit elements andwaveform follow. FIG. 2A of the drawing shows portions of a negative,composite video television signal 39 for controlling the timing of onefield of scan of the electron beam in a cathode-ray tube. The compositevideo signal is comprised of a serrated vertical synchronizing pulse 40,equalizing pulses 42 and horizontal synchronizing pulses 43.

A composite video signal of either positive or negative polarity can beapplied to input 15 of inverter 10. Transistor 112 redevelops thecomposite video signal with its original polarity across the emitterload resistor 122, which is connected through loading resistor 124 tooutput terminal 126. The composite video signal is developed in aninverted form across the collector load resistor 528 which is connectedto output tenninal 130. Consequently, if a composite video signal ofpositive polarity is applied to input 15 a composite video signal ofnegative polarity which is l80 out-of-phase therewith will be developedat output terminal 130. Alternatively, if a composite video signal ofnegative polarity is applied to input 15, it will reappear at outputterminal 126. Therefore, regardless of the polarity of the compositevideo signal at terminal 15 a composite video signal of negativepolarity will be available at either terminal 126 or 130.

Amplifier 12 includes transistor 132 which is biased to amplifycomposite video signals of negative polarity. Switch 134 can be operatedto select by means of selecting portion 136 the signal of negativepolarity from either terminal 126 or 130. This signal is amplified bytransistor I32 and a composite video signal of positive polarity isproduced at output terminal 138. Sync stripper 14 includes transistor140 which is biased substantially below cutoff. The base biasingnetwork, connected from base 142 of transistor I and output terminal 138of amplifier 12, is comprised of capacitor 144 and resistor 146. Thisbase biasing network in cooperation with the biasing resistors 148 and150, biases transistor so that it conducts only during the sync pulsesof the composite video signal. As a result, only the negative syncpulses 44, as shown in FIG. 2B, are present at output terminal 151 ofsync stripper 14. The foregoing circuitry, therefore, selects all thesync pulses from the composite video television signal.

These sync pulses are applied to input 16 of NAND gate 18 and to input152 of dual integrating network 20 which is comprised of a firstintegrating network, resistor 154 and capacitor 156, which is cascadedwith a second integrating network, resistor 158 and capacitor 160. Thisdual integrating network filters out the equalizing and horizontal syncpulses and allows only the vertical sync pulses to be applied throughthe parallel combination of resistor 162 and capacitor 164, and throughresistor 166, to the base or normally saturated transistor 168. Theparallel combination of capacitor and resistor 172, which are connectedto the emitter 173 of transistor 168, cooperate to remove the remains ofthe serrations not removed by the integrating circuit from the verticalsync pulse so that it appears at output terminal 174 with the form 45illustrated in FIG. 2C of the drawing.

Each positive-going vertical sync pulse 45 is differentiated bycapacitor 176 and resistor 178, of differentiator circuit 23, into apositive-going spike 47 of FIG. 2D, coincident with the leading edge 46thereof and a negative-going spike 49 coincident with the lagging edge48 thereof. The positive-going spikes are conducted to ground by diode180 and the negative-going spikes are coupled through capacitor 182 toturn off normally on transistor 184 thereby turning on normally offtransistor 186 of the first monostable or delay circuit 24. Transistor186 remains on for a predetermined adjustable recycle time which is afunction of the setting of rheostat 188. While transistor 184 is off apositive pulse 50 appears at the collector thereof as shown in FIG. 2E,whose duration A can be varied by adjusting rheostat 188.

Differentiating network 25, including capacitor 194 and resistor I96,differentiate each pulse 50 into a positive spike 51 and a negativespike 53 as shown in FIG. 2F. Diode 198 passes the negative-going spike53, which is coincident with the lagging edge 52 of pulse 50, throughcapacitor 200 to turn off normally on transistor 202 and turn onnormally off transistor 204 of second monostable or the enabling circuit26. As a result, a negative-going enable pulse 54, shown in FIG. 26, isdeveloped at output 206 of monostable 26 whose leading edge 56 iscoincident with lagging edge 52 of first timing pulse 50 and whoseduration B is a function of the setting of rheostat 208.

NAND gate 18 includes transistor 210 which is biased into a saturationso that the voltage level at output 212 is near ground or referencepotential unless there are simultaneous near zero potentials at input 16and 28. Consequently, when there is a simultaneous application theretoof the negativegoing enable pulse 54, through resistor 214, along withthe application of negative-going sync pulse or pulses 44, from output151 of sync stripper 14, transistor 210 is turned off in synchronism orcoincidence with the selected sync pulses occurring during the period ortime interval of pulse 54 which action results in selected positive syncpulses being developed at output 212. These positive sync pulses arecoupled to the external trigger input 30 of oscilloscope 32 so thatmonitored signals applied across vertical input terminals 33 and 35occurring in time relation with the selected sync signals can bedisplayed on the scope.

The foregoing described oscilloscope triggering circuitry has manyapplications. For instance, assume that it is desirable to periodicallytrigger oscilloscope 32 in synchronism with just horizontal sync pulses60 through 68 of FIG. 2H so that identical portions of a color bar videosignal, from within the circuitry of a TV receiver, corresponding tothese pulses would be retraced or superimposed on the screen of theoscilloscope to facilitate trace brightening so that their otherwiseindistinguishable details could be observed. In order to display thedesired portions, the composite color bar video signal from the colorbar generator could be applied to input of the triggering circuit andthe video from the receiver could be applied to vertical input terminals33 and 35 of the oscilloscope.

Next rheostat 188, of delay circuit 24, would be adjusted so that theedge 56 of the enabling pulse 54, shown in dotted lines 72 in FIG. 2H,occurs immediately prior to the leading edge 74 of horizontal sync pulse60. Then rheostat 208, of enable circuit 26, could be adjusted so thatthe lagging edge 76 of enabling signal 54 occurs after the fallingportion 78 of pulse 68. Consequently, only the portions of the videosignal occurring in time relation to these pulses will be superimposedon the face of the cathode-ray tube 80 of oscilloscope 32.

What has been described, therefore, is an oscilloscope triggeringcircuit which operates either on a composite video signal or on a trainof sync pulses to allow a selected sync pulse or group of successiveselected sync pulses to trigger an oscilloscope so that waveformsapplied to the input of the oscilloscope occurring in time relationtherewith can be displayed on the screen of the oscilloscope. There aremany applications related to the design and test of black and white andcolor television equipment where the described triggering circuit isparticularly useful.

lclaim:

l. A circuit for providing a trigger signal to trigger an oscilloscopefor display thereon of selected waveforms occurring in time relation toa pulse train of synchronization pulses for controlling the scan of anelectron beam in a cathode-ray tube, which triggering circuit providesthe trigger signal by allowing only selected synchronization pulses fromthe pulse train to be applied to the trigger input of the oscilloscope,such triggering circuit including in combination, first signal supplymeans providing synchronization pulses, first pulse producing circuitconnected to said first signal supply means and responsive to thetermination of each synchronization pulse to produce a delaying pulsehaving an adjustable duration, enable pulse producing circuit connectedto said first pulse producing circuit and responsive to the terminationof each of said delaying pulses to produce a delayed enabling pulse ofadjustable time duration, gating means having first input meansconnected to said enable pulse producing circuit and second input meansconnected to said first signal supply means, said gating means beingresponsive to the simultaneous application thereto of said enablingpulses and said synchronization pulses to pass therethrough only thoseselected synchronization'pulses occurring during the time interval ofsaid enabling pulses, conducting means connected between the output ofsaid gating means and'the trigger input of the oscilloscope for applyingthe selected synchronization pulses to trigger the oscilloscope therebyallowing waveforms occurring in time relation to the selectedsynchronization pulses to be displayed on the oscilloscope.

. 2. The triggering circuit of claim 1 wherein said first signal supplymeans includes in combination, a second signal supply means providing acomposite video television signal of either polarity, inverter meanshaving the input thereof connected to said second signal supply meansand having two output terminals at which are simultaneously producedcomposite video television signals which are 180 out-of-phase with eachother, sync stripper means responsive to composite video televisionsignals of one polarity to remove the synchronization pulses therefrom,switching means connected between said output terminals of said invertermeans and the input of said sync stripper means for selecting saidcomposite video television,

ses from said synchronization pulses provided thereby firstdifferentiating CllCLlll. means connected to the output 0 saidintegrating circuit means for providing a first differentiation pulsecoincident with the terminating portion of each of said verticalsynchronizing pulses, first monostable multivibrator means having anadjustable recycle time connected to the output of said firstdifferentiating circuit means, said first monostable multivibrator meansbeing responsive to each of said first differentiation pulses to producesaid delaying pulses having adjustable duration.

4. The triggering circuit of claim 1 wherein said enable pulse producingcircuit includes in combination, second differentiating circuit meansconnected to the output of said first pulse producing circuit forproviding a second differentiation pulse coincident with termination ofsaid delaying pulses, second monostable multivibrator means having anadjustable recycle time connected to the output of said second differentiating circuit, said second monostable multivibrator means beingresponsive to each of said second differentiation pulses to produce saiddelayed enabling pulse of adjustable time duration.

5. A triggering circuit for providing a trigger signal to trigger anoscilloscope for display thereon of selected waveforms occurring in timerelation to a pulse train of synchronization pulses which triggeringcircuit provides the trigger signal by allowing only selectedsynchronization pulses from the composite video television signal to beapplied to the trigger input of the oscilloscope, such triggeringcircuit including in combination, signal supply means providing thecomposite video television signal, sync stripping means connected to theoutput of said signal supply means for removing the synchronizationpulses from the composite video television signal, first pulse producingcircuit connected to said sync stripping means and responsive to thetermination of pulses synchronization pulse to produce a delaying pulsehaving an adjustable duration, enable pulse producing circuit connectedto said first pulse producing circuit and responsive to the terminationof each of said delaying pulses to produce an enabling pulse ofadjustable time duration, gating means having first input meansconnected to said enable pulse producing circuit and second input meansconnected to said sync stripping means, said gating means beingresponsive to simultaneous application thereto of said enabling pulseand said synchronization pulses topass therethrough only thosesynchronization pulses occurring during the time interval of saidenabling pulse, conducting means connected between the output of saidgating means and the trigger input of the oscilloscope for applying theselected synchronization pulses to trigger the oscilloscope therebyallowing waveforms occurring in time relation to the selectedsynchronization pulses to be displayed on the oscilloscope.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 573,538 Datedmupm fl Inventor(s) Roger A, Swanberq It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 1, cancel "invention" after SUMMARY OF TE INVENTION.Column 6, line 7, delete "first"; line 10, insert a comma after"combination"; line 45, delete "pulses' substitute predeterminedtherefor; line 45, at the end of the line, delete "pulse" and substitutepulses there Signed and sealed this 10th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents =0RM PO-105O (10-69) USCOMM-DC e031

1. A circuit for providing a trigger signal to trigger an oscilloscope for display thereon of selected waveforms occurring in time relation to a pulse train of synchronization pulses for controlling the scan of an electron beam in a cathode-ray tube, which triggering circuit provides the trigger signal by allowing only selected synchronization pulses from the pulse train to be applied to the trigger input of the oscilloscope, such triggering circuit including in combination, first signal supply means providing synchronization pulses, first pulse producing circuit connected to said first signal supply means and responsive to the termination of each synchronization pulse to produce a delaying pulse having an adjustable duration, enable pulse producing circuit connected to said first pulse producing circuit and responsive to the termination of each of said delaying pulses to produce a delayed enabling pulse of adjustable time duration, gating means having first input means connected to said enable pulse producing circuit and second input means connected to said first signal supply means, said gating means being responsive to the simultaneous application theReto of said enabling pulses and said synchronization pulses to pass therethrough only those selected synchronization pulses occurring during the time interval of said enabling pulses, conducting means connected between the output of said gating means and the trigger input of the oscilloscope for applying the selected synchronization pulses to trigger the oscilloscope thereby allowing waveforms occurring in time relation to the selected synchronization pulses to be displayed on the oscilloscope.
 2. The triggering circuit of claim 1 wherein said first signal supply means includes in combination, a second signal supply means providing a composite video television signal of either polarity, inverter means having the input thereof connected to said second signal supply means and having two output terminals at which are simultaneously produced composite video television signals which are 180* out-of-phase with each other, sync stripper means responsive to composite video television signals of one polarity to remove the synchronization pulses therefrom, switching means connected between said output terminals of said inverter means and the input of said sync stripper means for selecting said composite video television signals of said one polarity from said inverter means and for applying them to said sync stripper means which removes the synchronization pulses therefrom.
 3. The triggering circuit of claim 1 wherein said first synchronization pulses include vertical synchronization pulses and wherein said first pulse producing circuit includes in combination integrating circuit means connected to said first signal supply means to separate the vertical synchronizing pulses from said synchronization pulses provided thereby, first differentiating circuit means connected to the output of said integrating circuit means for providing a first differentiation pulse coincident with the terminating portion of each of said vertical synchronizing pulses, first monostable multivibrator means having an adjustable recycle time connected to the output of said first differentiating circuit means, said first monostable multivibrator means being responsive to each of said first differentiation pulses to produce said delaying pulses having adjustable duration.
 4. The triggering circuit of claim 1 wherein said enable pulse producing circuit includes in combination, second differentiating circuit means connected to the output of said first pulse producing circuit for providing a second differentiation pulse coincident with termination of said delaying pulses, second monostable multivibrator means having an adjustable recycle time connected to the output of said second differentiating circuit, said second monostable multivibrator means being responsive to each of said second differentiation pulses to produce said delayed enabling pulse of adjustable time duration.
 5. A triggering circuit for providing a trigger signal to trigger an oscilloscope for display thereon of selected waveforms occurring in time relation to a pulse train of synchronization pulses which triggering circuit provides the trigger signal by allowing only selected synchronization pulses from the composite video television signal to be applied to the trigger input of the oscilloscope, such triggering circuit including in combination, signal supply means providing the composite video television signal, sync stripping means connected to the output of said signal supply means for removing the synchronization pulses from the composite video television signal, first pulse producing circuit connected to said sync stripping means and responsive to the termination of pulses synchronization pulse to produce a delaying pulse having an adjustable duration, enable pulse producing circuit connected to said first pulse producing circuit and responsive to the termination of each of said delaying pulses to produce an enabling pulse of adjustable time duration, gating means having first input means connected to said enable puLse producing circuit and second input means connected to said sync stripping means, said gating means being responsive to simultaneous application thereto of said enabling pulse and said synchronization pulses to pass therethrough only those synchronization pulses occurring during the time interval of said enabling pulse, conducting means connected between the output of said gating means and the trigger input of the oscilloscope for applying the selected synchronization pulses to trigger the oscilloscope thereby allowing waveforms occurring in time relation to the selected synchronization pulses to be displayed on the oscilloscope. 